Ceramic Resonators (CERALOCK®) FAQ

Operation Circuit

Please explain noise-suppressing measures.

The CERALOCK® provides lower Q than quartz resonators, and large capacitance between terminals. Therefore, the noise (unwanted radiation noise) affecting the CERALOCK® is lower than that for quartz resonators. If you still have a problem with noise on the CERALOCK®, you can suppress the noise to some extent by changing the constants of the oscillation circuit. For this purpose, the following three methods are commonly used:

Increase the load capacitance.

If the load capacitance is increased, the effect of the low-pass filter will be enhanced, causing the microwave noise to be reduced. In this case, however, the oscillation frequency will be slightly reduced. If the load capacitance is increased too much, oscillation will stop.

Add a damping resistor (Rd).

Adding a damping resistor further enhances the load capacitance and the effect of the low-pass filter, and also corrects the matching between the CERALOCK® and the IC being used, enabling the reflective ringing to be suppressed. Also, this can reduce current consumption, resulting in noise suppression. If the damping resistance is increased too much, oscillation will stop.

Insert ferrite beads between the load capacitance and GND.

Inserting ferrite beads lowers the microwave gain, resulting in noise suppression. If the inductance or loss from the ferrite beads is too large, oscillation stop or abnormal oscillation may occur.

Even if you use any of the above methods 1) to 3), it may not be effective in noise suppression, depending on the IC and CERALOCK® being used. Particularly, with the CERALOCK® using 3rd-overtone oscillation, the circuit constants provide little oscillation excess gain, and you must thoroughly consider the circuit constants.